Incremental PCA algorithm for fringe pattern demodulation.

This work proposes a new algorithm for demodulating fringe patterns using principal component analysis (PCA). The algorithm is based on the incremental implantation of the singular value decomposition (SVD) technique for computing the principal values associated with a set of fringe patterns. Instead of processing an entire set of interferograms, the proposed algorithm proceeds in an incremental way, processing sequentially one (as minimum) interferogram at a given time. The advantages of this procedure are twofold. Firstly, it is not necessary to store the whole set of images in memory, and, secondly, by computing a phase quality parameter, it is possible to determine the minimum number of images necessary to accurately demodulate a given set of interferograms. The proposed algorithm has been tested for synthetic and experimental interferograms showing a good performance.

Sociodemographic and work environment correlates of missed nursing care at highly specialized hospitals in Mexico: A cross-sectional study.

BACKGROUND: Despite its direct relevance to quality of care, little is known about missed nursing care or its sociodemographic and work environment correlates at highly specialized hospitals in low- and middle-income countries. OBJECTIVE: To analyze the frequency of missed nursing care among Mexican nursing professionals, and to assess its associated sociodemographic and labor-related predictors. DESIGN AND METHODS: A cross-sectional, observational study based on data collected from 315 nursing professionals in 11 highly specialized public hospitals in Mexico. We assessed missed nursing care both as a total figure and according to the four dimensions of the MISSCARE inventory. We estimated its sociodemographic and work-related predictors using fractional logistic analysis. RESULTS: The global score for missed nursing care was 15.21%: 7.94% concerned individual needs, 9.37% discharge planning and patient education, 18.10% basic care, and 1.59% care under continuous assessment. The odds of engaging in missed nursing care increased with age and were higher among women and night-shift workers. In contrast, they decreased among nursing professionals who were satisfied with their jobs, and among those working in suitable environments. CONCLUSIONS: Missed nursing care in highly specialized public hospitals is associated with the sociodemographic characteristics and labor-related conditions -including the work environments- of the nurses. Given its impact on both health-care users and institutions, further research on the subject is urgently needed. It is essential to improve the design, implementation and evaluation of comprehensive strategies aimed at reducing the frequency of missed nursing care and achieving universal health coverage.

Robust weighted principal components analysis demodulation algorithm for phase-shifting interferometry.

We present an asynchronous phase-shifting demodulation approach based on the principal component analysis demodulation method that is robust to typical problems as turbulence, vibrations, and temporal instabilities of the optical setup. The method brings together a two-step and a phase-shifting asynchronous demodulation method to share their benefits while reducing their intrinsic limitations. Thus, the proposed approach is based on a two-fold process. First, the modulating phase is estimated from a two-step demodulation approach. Second, this information is used to compute weights to each phase-shifted pattern of the interferogram sequence, which are used in a novel weighted principal component demodulation approach. The proposed technique has been tested with simulated and real interferograms affected by turbulence and vibrations providing very satisfactory results in challenging cases.

Nursing before COVID-19, a key point for the prevention, control and mitigation of the pandemic.

The SARS-CoV-2 or COVID-19 outbreak originated in China has reached Mexico. However, the scientific community, including nursing, has generated vertiginous evidence that can help make decisions in the care of the affected population. The purpose of this study is to describe the nursing experience before COVID-19 as a key point for the prevention, control and mitigation of the pandemic. Based on the recommendations issued by the Ministry of Health, the clinical evidence and the resources available in the health institutions, the disease prevention measures have been initiated and maintained both in the community and in the health institutions. The reconversion of hospitals and care protocols adapted to our context are trying to strengthen the control and mitigation of the disease.

El brote de SARS-CoV-2 o COVID-19 originado en China ha alcanzado a México; no obstante, la comunidad científica, entre ellas enfermería ha generado de forma vertiginosa evidencia que puede ayudar a tomar decisiones en la atención de la población afectada. El presente documento tiene la finalidad de describir la experiencia de enfermería ante el COVID-19 como un punto clave para la prevención, control y mitigación de la pandemia. Con base en las recomendaciones emitidas por la Secretaría de Salud, la evidencia clínica y los recursos disponibles en las instituciones de salud se ha iniciado y mantenido las medidas de prevención de la enfermedad tanto en la comunidad como en las instituciones de salud. La reconversión de los hospitales y los protocolos de atención adaptados a nuestro contexto están tratando de fortalecer el control y mitigación de la enfermedad.

Enfermería ante el COVID-19, un punto clave para la prevención, control y mitigación de la pandemia / Nursing before COVID-19, a key point for the prevention, control and mitigation of the pandemic

Resumen El brote de SARS-CoV-2 o COVID-19 originado en China ha alcanzado a México; no obstante, la comunidad científica, entre ellas enfermería ha generado de forma vertiginosa evidencia que puede ayudar a tomar decisiones en la atención de la población afectada. El presente documento tiene la finalidad de describir la experiencia de enfermería ante el COVID-19 como un punto clave para la prevención, control y mitigación de la pandemia. Con base en las recomendaciones emitidas por la Secretaría de Salud, la evidencia clínica y los recursos disponibles en las instituciones de salud se ha iniciado y mantenido las medidas de prevención de la enfermedad tanto en la comunidad como en las instituciones de salud. La reconversión de los hospitales y los protocolos de atención adaptados a nuestro contexto están tratando de fortalecer el control y mitigación de la enfermedad.

Abstract The SARS-CoV-2 or COVID-19 outbreak originated in China has reached Mexico. However, the scientific community, including nursing, has generated vertiginous evidence that can help make decisions in the care of the affected population. The purpose of this study is to describe the nursing experience before COVID-19 as a key point for the prevention, control and mitigation of the pandemic. Based on the recommendations issued by the Ministry of Health, the clinical evidence and the resources available in the health institutions, the disease prevention measures have been initiated and maintained both in the community and in the health institutions. The reconversion of hospitals and care protocols adapted to our context are trying to strengthen the control and mitigation of the disease.

Reconstruction of local frequencies for recovering the unwrapped phase in optical interferometry.

In optics, when interferograms or digital holograms are recorded and their phase is recovered, it is common to obtain a wrapped phase with some errors, noise and artifacts such as singularities due to the non linearities of the demodulation process. This paper shows how to reconstruct the frequency field of the wrapped phase by using adaptive Gabor filters. Gabor filters are Gaussian quadrature filters tuned in at a certain frequency. We adapt these Gabor filters by tuning them locally and estimating the frequency using wrapped finite differences of the estimated phase. Doing this process iteratively, the frequency estimation is refined and smoothed. The unwrapped phase is easily recovered by integrating the recovered frequency field using, for example, a simple line raster integration. We don't have problems with phase inconsistencies or residues while integrating the phase, because these are removed. The obtained unwrapped phase is clean, consistent and practically error-free. We show estimation errors with simulated data and the performance of the proposed method using real-world recorded wavefronts.

Volume estimation of tonsil phantoms using an oral camera with 3D imaging.

Three-dimensional (3D) visualization of oral cavity and oropharyngeal anatomy may play an important role in the evaluation for obstructive sleep apnea (OSA). Although computed tomography (CT) and magnetic resonance (MRI) imaging are capable of providing 3D anatomical descriptions, this type of technology is not readily available in a clinic setting. Current imaging of the oropharynx is performed using a light source and tongue depressors. For better assessment of the inferior pole of the tonsils and tongue base flexible laryngoscopes are required which only provide a two dimensional (2D) rendering. As a result, clinical diagnosis is generally subjective in tonsillar hypertrophy where current physical examination has limitations. In this report, we designed a hand held portable oral camera with 3D imaging capability to reconstruct the anatomy of the oropharynx in tonsillar hypertrophy where the tonsils get enlarged and can lead to increased airway resistance. We were able to precisely reconstruct the 3D shape of the tonsils and from that estimate airway obstruction percentage and volume of the tonsils in 3D printed realistic models. Our results correlate well with Brodsky's classification of tonsillar hypertrophy as well as intraoperative volume estimations.

High-resolution low-noise 360-degree digital solid reconstruction using phase-stepping profilometry.

In this paper we describe a high-resolution, low-noise phase-shifting algorithm applied to 360 degree digitizing of solids with diffuse light scattering surface. A 360 degree profilometer needs to rotate the object a full revolution to digitize a three-dimensional (3D) solid. Although 360 degree profilometry is not new, we are proposing however a new experimental set-up which permits full phase-bandwidth phase-measuring algorithms. The first advantage of our solid profilometer is: it uses base-band, phase-stepping algorithms providing full data phase-bandwidth. This contrasts with band-pass, spatial-carrier Fourier profilometry which typically uses 1/3 of the fringe data-bandwidth. In addition phase-measuring is generally more accurate than single line-projection, non-coherent, intensity-based line detection algorithms. Second advantage: new fringe-projection set-up which avoids self-occluding fringe-shadows for convex solids. Previous 360 degree fringe-projection profilometers generate self-occluding shadows because of the elevation illumination angles. Third advantage: trivial line-by-line fringe-data assembling based on a single cylindrical coordinate system shared by all 360-degree perspectives. This contrasts with multi-view overlapping fringe-projection systems which use iterative closest point (ICP) algorithms to fusion the 3D-data cloud within a single coordinate system (e.g. Geomagic). Finally we used a 400 steps/rotation turntable, and a 640x480 pixels CCD camera. Higher 3D digitized surface resolutions and less-noisy phase measurements are trivial by increasing the angular-spatial resolution and phase-steps number without any substantial change on our 360 degree profilometer.

Robust adaptive phase-shifting demodulation for testing moving wavefronts.

Optical interferometers are very sensitive when environment perturbations affect its optical path. The wavefront under test is not static at all. In this paper, it is proposed a novel and robust phase-shifting demodulation method. This method estimates the interferogram's phase-shifting locally, reducing detuning errors due to environment perturbations like vibrations and/or miscalibrations of the Phase-Shifting Interferometry setup. As we know, phase-shifting demodulation methods assume that the wavefront under test is static and there is a global phase-shifting for all pixels. The demodulation method presented here is based on local weighted least-squares, letting each pixel have its own phase-shifting. This is a different and better approach, considering that all previous works assume a global phase-shifting for all pixels of interferograms. Seeing this method like a black box, it receives an interferogram sequence of at least 3 interferograms and returns the modulating phase or wavefront under test. Here it is not necessary to know the phase shifts between the interferograms. It does not assume a global phase-shifting for the interferograms, is robust to the movements of the wavefront under test and tolerates miscalibrations of the optical setup.

Windowed phase unwrapping using a first-order dynamic system following iso-phase contours.

In this work, we show a windowed phase-unwrapping technique that uses a first-order dynamic system and scans the phase following its iso-phase contours. In previous works, we have shown that low-pass first-order dynamic systems are very robust and useful in phase-unwrapping problems. However, it is well known that all phase-unwrapping methods have a minimum signal-to-noise ratio that they tolerate. This paper shows that scanning the phase within local windows and using a path following strategy, the first-order unwrapping method increases its tolerance to noise. In this way, using the improved approach, we can unwrap phase maps where the basic dynamic phase-unwrapping system fails. Tests and results are given, as well as the source code in order to show the performance of the proposed method.

Fast two-dimensional simultaneous phase unwrapping and low-pass filtering.

Here, we present a fast algorithm for two-dimensional (2D) phase unwrapping which behaves as a recursive linear filter. This linear behavior allows us to easily find its frequency response and stability conditions. Previously, we published a robust to noise recursive 2D phase unwrapping system with smoothing capabilities. But our previous approach was rather heuristic in the sense that not general 2D theory was given. Here an improved and better understood version of our previous 2D recursive phase unwrapper is presented. In addition, a full characterization of it is shown in terms of its frequency response and stability. The objective here is to extend our previous unwrapping algorithm and give a more solid theoretical foundation to it.

Noise robust linear dynamic system for phase unwrapping and smoothing.

Phase unwrapping techniques remove the modulus ambiguities of wrapped phase maps. The present work shows a first-order feedback system for phase unwrapping and smoothing. This system is a fast sequential unwrapping system which also allows filtering some noise because in deed it is an Infinite Impulse Response (IIR) low-pass filter. In other words, our system is capable of low-pass filtering the wrapped phase as the unwrapping process proceeds. We demonstrate the temporal stability of this unwrapping feedback system, as well as its low-pass filtering capabilities. Our system even outperforms the most common and used unwrapping methods that we tested, such as the Flynn's method, the Goldstain's method, and the Ghiglia least-squares method (weighted or unweighted). The comparisons with these methods shows that our system filters-out some noise while preserving the dynamic range of the phase-data. Its application areas may cover: optical metrology, synthetic aperture radar systems, magnetic resonance, and those imaging systems where information is obtained as a demodulated wrapped phase map.

A self-tuning phase-shifting algorithm for interferometry.

In Phase Stepping Interferometry (PSI) an interferogram sequence having a known, and constant phase shift between the interferograms is required. Here we take the case where this constant phase shift is unknown and the only assumption is that the interferograms do have a temporal carrier. To recover the modulating phase from the interferograms, we propose a self-tuning phase-shifting algorithm. Our algorithm estimates the temporal frequency first, and then this knowledge is used to estimate the interesting modulating phase. There are several well known iterative schemes published before, but our approach has the unique advantage of being very fast. Our new temporal carrier, and phase estimator is capable of obtaining a very good approximation of their temporal carrier in a single iteration. Numerical experiments are given to show the performance of this simple yet powerful self-tuning phase shifting algorithm.